Testing POST with request body in Express - Mini Project: Build & Apply

Testing POST with request body in Express

📖 Scenario: You are building a simple Express server that accepts user data via a POST request. You want to write a test to check that the server correctly receives and processes the JSON data sent in the request body.

🎯 Goal: Create a test for an Express POST route that sends a JSON body and verifies the server response.

📋 What You'll Learn

Create an Express app with a POST route at /users

Use express.json() middleware to parse JSON request bodies

Write a test that sends a POST request with a JSON body containing {"name": "Alice", "age": 30}

Verify the server responds with status 201 and a JSON message confirming user creation

💡 Why This Matters

🌍 Real World

Testing POST requests with JSON bodies is common when building APIs that accept user data, such as registration forms or data submission endpoints.

💼 Career

Backend developers and QA engineers often write tests like this to ensure API endpoints work correctly and handle data as expected.

1

Set up Express app with POST route

Create an Express app in a variable called app. Add a POST route at /users that responds with status 201 and JSON { message: "User created" }. Use express.json() middleware to parse JSON bodies.

Express

const express = require('express');
const app = express();
// Your code here

Need a hint?

Remember to use express.json() middleware before defining the POST route.

2

Set up test environment with supertest

Create a variable called request that requires supertest and wraps the app variable for testing HTTP requests.

Express

const express = require('express');
const app = express();
app.use(express.json());
app.post('/users', (req, res) => {
  res.status(201).json({ message: "User created" });
});

const supertest = require('supertest');
// Your code here

Need a hint?

Use supertest to wrap your Express app for testing.

3

Write test sending POST request with JSON body

Write an async test function called testCreateUser that sends a POST request to /users with JSON body { name: "Alice", age: 30 } using request.post. Await the response and store it in a variable called response.

Express

const express = require('express');
const app = express();
app.use(express.json());
app.post('/users', (req, res) => {
  res.status(201).json({ message: "User created" });
});

const supertest = require('supertest');
const request = supertest(app);

async function testCreateUser() {
  // Your code here
}

Need a hint?

Use request.post('/users').send({ name: "Alice", age: 30 }) and await the response.

4

Verify response status and JSON message

Inside the testCreateUser function, add assertions to check that response.status equals 201 and response.body.message equals "User created".

Express

const express = require('express');
const app = express();
app.use(express.json());
app.post('/users', (req, res) => {
  res.status(201).json({ message: "User created" });
});

const supertest = require('supertest');
const request = supertest(app);

async function testCreateUser() {
  const response = await request.post('/users').send({ name: "Alice", age: 30 });
  // Add assertions here
}

Need a hint?

Use simple if statements to check response.status and response.body.message.